> ---------------------------------------------------------------------- > > On Mon, 4 Feb 2008 18:16:19 +0100, Miklos Szigetvari wrote: > > >Hi > > > >I got this question time to time: > >What is the maximum CPU time difference for the same job, between > >repeated runs, under different system load ? > > ---------------------------------------------------------------------- > > On Mon, 4 Feb 2008 11:51 (CST USA), Tom Marchant wrote: > > Maximum? One could be several times another. > > Why? One time, with little significant contention, almost all the date > referenced is in the High Speed Buffer (or cache) and all virtual address > translations are handled in the TLB. Worst case is that almost all memory > references cause a HSB miss and the TLB entries are no longer there when > they are needed. A memory reference takes several times as long when the > data is not in the cache. And if the Translation Lookaside Buffer does > not > have the information required to translate the virtual address to a real > address, that will require a segment table and page table reference, again > with > the possibility of HSB misses. If the reference is above the bar, there > may > well be region table references as well. > > -- > Tom Marchant > > ---------------------------------------------------------------------- Am I missing something here? Miklos is asking about the difference in CPU time between two runs of the same job step. I would think that if the same program was processing the same data in the same way the CPU time should be close to consistent. Maybe not exactly the same but there shouldn't be "several times another". Now the elapsed time could vary widely depending on the contentions that Tom has mentioned above.
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